Antireflection members such as antireflection film are provided at the outermost surface of image display apparatuses including cathode ray tube (CRT), plasma display panel (PDP), and liquid crystal display (LCD). In an antireflection film, the reflectance is reduced according to the principle of optical interference to prevent contrast reduction and reflected images from resulting from the reflection of outside light.
Some antireflection members with improved scratch resistance and abrasion resistance have been proposed as follows.
In a proposal, a coating layer consisting of a multifunctional (meth)acrylic compound and a fluorochemical surfactant mixed at a ratio of 99.9:0.1 to 90:10 (by mass) is cured to produce an antireflection film having the cured layer as the outermost layer (JP 2008-122603 A).
Another proposal offers an antireflection material consisting of a hard coat layer produced by curing a resin composition comprising electrically conductive ultrafine inorganic particles and a radiation curing type resin and a layer with a low refractive index containing fine hollow silica particles, which are stacked on a substrate. The resin composition for this hard coat layer contains at least one resin component that has a mass average molecular weight of 8,000 or more and 150,000 or less (JP 2007-271954 A).
Production methods as described below have been proposed to provide a simplified antireflection member production processes.
A proposal offers an antireflection layer production method that comprises the step of forming one coat of a coating composition consisting of fine particles with a low refractive index and fine particles with a medium to high refractive index dispersed in a binder resin. In this method, fine silica particles treated with a fluorine-based compound are used as the fine particles with a low refractive index. Due to a difference in specific gravity, fine particles with a lower refractive index are more abundant in the top to central portions of the antireflection layer while fine particles with a higher refractive index are more abundant in the central to bottom portions (JP 2007-272132 A).
In another proposal, a coat of a paint composition is spread over at least one face of a support substrate and dried to produce an antireflection film comprising two layers that have different refractive indices. This paint composition is characterized by containing two or more kinds of inorganic particles and a metal chelate compound, with at least one kind of inorganic particles surface-treated with a fluorine-based compound (JP 2009-058954 A).
Described below are proposals of antireflection members that focus on the function of the interlayer interface between layers that constitute an antireflection member.
A proposed optical film consists of a first transparent layer and a second transparent layer adjacent to each other, wherein the first transparent layer and the second transparent layer have different refractive indices and the contact interface between the first transparent layer and the second transparent layer scatters light. As light is scattered at the contact interface between the first transparent layer and the second transparent layer, the formation of interference fringes is depressed to allow the film to act as an optical film (JP 2005-107005 A).
An antireflection film having an electrically conductive transparent layer, hard coat layer with a high refractive index, and hard coat layer with a low refractive index formed in this order on its surface has been proposed. In this antireflection film, the roughness of the interface between the hard coat layer with a high refractive index and the hard coat layer with a low refractive index is lower than that of the interface between the electrically conductive transparent layer and the hard coat layer with a high refractive index, and the hard coat layer with a high refractive index and/or the hard coat layer with a low refractive index are formed of an organic and/or inorganic hybrid hard coat (JP 2004-258209 A).
It could therefore be helpful to provide an antireflection member that has the characteristics of high adhesiveness, scratch resistance, abrasion resistance and low interference irregularity, as well as the characteristics of low reflectance and high transparency.
The antireflection members proposed in JP '603 and JP 2007-271954 A require a hard coat layer of 2.5 μm or more and 5 μm or less to have high scratch resistance. In addition, coating operation is performed twice or three times to form two or more layers, including the hard coat layer, on a substrate. Thus, it will be difficult to produce these antireflection members in a simplified production process that requires both less material cost and a less number of steps.
In JP '603, a fluorochemical surfactant is added to reduce the surface free energy and a multifunctional acrylate is added to increase the crosslink density with the aim of ensuring that good adhesion properties, high scratch resistance, and high abrasion resistance are achieved together with low reflectance and high transparency. However, they fail to have sufficient effects. In addition, the fluorochemical surfactant is not fixed on the antireflection layer through chemical bonds, often causing the problem of transfer of the fluorochemical surfactant to other layers in the antireflection film. In JP '603, furthermore, no means are shown to depress interference irregularity.
The antireflection material proposed in JP 2007-271954 A has a wear resistant only enough to allow the layer with a lower refractive index in the antireflection material to slide to and fro 100 times under a load of 1 Kg. This level of abrasion resistance is lower than required for several times of cleaning operations that are considered necessary at present.
For the antireflection layer proposed in JP '132, coating operation is performed only once to produce a low refractive index layer and a high refractive index layer to constitute the antireflection layer. In JP '132, it is described that the low refractive index layer and the high refractive index layer do not form a distinct interface but merge with each other, thereby solving the problem of separation between these layers with different refractive indices more effectively than an antireflection layer with a distinct interface. It is expected, however, that the distinct interface between merged layers leads to a lower reflectance and transparency.
In JP 2009-058954 A, it is described that the two layers with different refractive indices have a distinct interface. However, the structure of the interface is not described in detail.
JP '005 and JP '209 focus on the function of the interface between layers that constitute an antireflection member, but its aim is to reduce interference pattern formation and prevent whitening. Furthermore, the layers that correspond to the low refractive index layer and high refractive index layer have a rough interface. This roughness serves to depress interference irregularity, but the interface scatters light, thereby decreasing the transparency.